Elements for use in the electrodeposition of chromium



March 2,` 2,072,l7

ELEMENTS FOR usElN THE ELEcTRoDEPoslTioN oF CHROMIUM vc5, K. HERZOGFiled NOV. 20, 1934 ,imp

nani/murs ron 'osu in 'run Etneo n nnrosrrion or nunon/univr e George K.llierzog, New Rochelle, N. Y., assigner to lilnited Chromium,incorporated, New orlt, N. Y., a corporation of Delaware 'appiieauoninventer to, 193i, senat no. 'Itasca n,` l Claims.

y\ *I This invention relates toa method,papparatus and elements thereoffor use in the electrodeposition of chromium and provides improvementstherein..

insulator which would be highly resistant to plating solutionscontaining chromic acid and be more satisfactory and serviceable thanthose heretofore used.. Insulators, or coatings thereof'are usedA p inthe artof chromium plating, for example,` to

hold conducting parts of opposite polarity in` spaced relation in orabove the solution, to insulate parts of conductors and racks immersedin the solution, to stopi4 or inhibit the flow of plating current' toparts of cathodes on which it is `desired not to have a plate, forlining containers to hold the plating solution, etc. The mostsatisfactory insulators heretofore discovered and now used are glass,ceramics, certain rubber prod- The word Bakelite is understood to be atrade-mark of the. corporation making and sellingl the resin, whichresin is a. condensation product forme from phenol and ormaldehyde.

ose products. Glass and. ceramics are of limited application becausethey are dimcult to work, and l re fragile. Rubber reacts with theplating soluion, disturbing its compositionin several ways, the rubberreducing the chromic acid to various trivalent chromium compounds andfouling kthe solution, and the .sulphur increasing the acid- `radicalcontentby being oxidized to sulphuric acid radical. Bakelite is verybrittle, dimcult to work and therefore of limited application. Whenfillers are incorporated in the Bakelite to reduce brittleness andincrease workability, the

resulting product is readily attacked by the plating solution. causingfouling of the solution and destroying lthe insulator. Films of Bakeliteor oi cellulose compounds 'resulting from the drying of liquid coats ofthe dissolved materials also react with the plating solution,reducing'the chromic acid and fouling the solution; the lms are brittleand swell and, increase in brittleness after exposure tov chromic acidsolution, and the parts of conductors` and racks to whichthese coatingsare applied have to be recoated. at frequent intervals, the practiceinmany plants being` to applycoats of the solution on weakened p areasof theracksat Ythe end of each day preparatorv to use the next day.Furthermore, it

lms of grease or` dirt on` articles to be chro mersing the rackscontaining the work to be cleaned into hot alkaline solutions. Bakelitelms break down very rapidly `when immersed in hot alkaliner solutions.`Cellulose products and ucts, Bakeliteml condensation-resin, and cellu-`mium plated by iirstracking them and then infrfilms thereof behavesimilarly to Bakelite and have the same shortcomings.

The most satisfactory containers heretofore usedior plating solutionscontaining chromicacidare lead or lead-alloy lined containers, and glassor ceramic containers. The lead-lined containers are conducting and somecurrent will flow to them resulting in objectionable stray currentedects. A disadvantage of stray currents, for instance, ls the shadingeect which occins when an article is placed too close to the conductinglining, some of the current intended for plating going to the lining,and not enough going to the article, so that the part'of the articleadjacent to the lining is not plated or is improperly plated., Lead isalso very heavy and is subject to attack by the solution, lead chromatebel ing formed, which results in failure ofthe linings and in theformation of Aan undesirable sludge in the solution. lCertainlead-alloys overcome the attack to a considerable extent. Glass andceramic containers are heavy, fragile, and expensive, and they areprincipally used where the bath is of small capacity.

By the present invention I provide apparatus and elements thereof of aninsulating character, or havinginsulating parts, which are highlyresistant to attack by warm or cold chromium .plat- 'ing solutionscontaining chromic acid, which give superior service as insulation inthe special use with these chromium-plating solutions, and which allowthe plating process to be carried out without the composition of thesolution being aleeted .or the solution fouled; and the invention alsoprovides a method of applying such insulation.

` By the present invention I furthermore provide containers, etc. whichare highly resistant to attack by warm or vcold plating solutionscontaining chromic acid, which are of reduced weight as compared withmetal, glass or ceramic containers, and which enable the process ofplating to be carried out without the disadvantages of stray currenteffects.

v One of the usually given properties ci chroniic:

acid is that of its attack on, and reduction. by, organic substances* Itis therefore a surprising pound polymers which I have found suitable arethose which from the physical standpoint are solid and tough. As most ofthe polymerizationproducts of the common vinyl compounds are either toosoft or too brittle, the desired physical properties may be obtained inthe conjoint polymerization product of two different vinyl compounds (bywhich is meant polymerization of two or more compounds while in mutualcontact); one compound (a vinyl halide, as vinyl chloride, for example,or vinyl benzene (styrene), for example) being one which, whenseparately polymerized, forms a hard resin, and the other compound (anester of a lower aliphatic acid, as vinyl acetate, vinyl propionate,vinyl butyrate, for example) being one which, when separatelypolymerlzed, forms a soft resin.

'I'hese conjoint polymerization products or resins are made and sold byCarbide & Carbon Chemicals Corporation, 30 East 42nd Street, New Yorkcity. However, those conjoint polymerization products in which theproportion of the vinyl ester of the soft resin forming type is toogreat, may tend to hydrolyze, or are less resistant for some otherreason, and therefore the vinyl ester of the soft resin forming typeshould be about equal to, and preferably less than, the vinyl compoundof the hard resin forming type. That is, the range of the proportions ofthe two types of cornpounds in the conjoint polymerization product(calculated as the monomeric compounds however present in the resin)should be 50 to 95 parts of the vinyl compound of the hard resin formingtype to 50 to 5 parts of the vinyl ester of the soft resin forming type.The optimum conjoint polymerization resin is one having 85 to 87 parts,of a total of D parts, of the vinyl compound of the hard resin formingtype, and to 13 parts of the vinyl ester of the soft resin forming type,calculated as explained above; and when parts of one or the other vinylcompounds are referred to herein, the word will be understood as beingused in the sense explained above.

According to my invention, I make apparatus and elements, and theinsulating parts thereof, to be used in contact with chromium platingsolutions of a conjoint polymerization resin as herein described.

Embodiments of the invention are illustrated in the accompanyingdrawing, wherein;

Fig. 1 is a view principally in side elevation, but with parts insection, illustrating the invention in the form of a rack with anauxilary anode.

Fig. 2 is a view partly in side elevation and partly in section,illustrating the invention in the form of a rack or xture for plating anarticle with stops applied thereto.

Fig. 3 is a view in side elevation illustrating the invention in theform of a rack for holding a number of articles to be plated.

Fig. 4 is a view in cross-section of a plating tank according to thepresent invention.

Referring to said drawing, numeral I0 designates insulation of conjointpolymerization resin according to the present invention applied in avariety of ways to apparatus and elements, and to parts thereof.

Referringto Fig.` l, numeral I2 designates an auxiliary anode(conducting) which may be, as here shown, connected to the same anodebus-bar as the normal anode I4. I6 designates a conducting-rod which isconnected to the cathode busbar and which supports the article C to beplated, the article being illustrated as a part of an icecream scoop,and as connected to a threaded stud I8 projecting from the rod I6. Theposition of the auxiliary anode I2 with relation to the cathode-articleC is a more or less precise one, and so as to avoid the labor and careof positioning the auxiliary anode I 2 for each plating operation, Vtheauxiliary anode I2 and the cathode-rod I6 are mounted in fixed relationin a blockZD. The block 20, connecting the parts I2 and I6 of oppositepolarity, is made of insulation of the herein described kind. 'I'he rackor xture shown in Fig. 1, when used for plating in a chromium platinginstallation, projects partly below the surface of the plating bath, theimmersed part being below the solution level indicated in the gure. Theparts I2 and I6 being conductors having opposite polar-,l

ity, the parts below the solution level should beinsulated so thatcurrent will not ow directly from one part to the other. To prevent suchcurrent flow, insulation of the herein described kind in the form of atube or sleeve 22fis applied to the vertical length of the auxiliaryanode I2, and insulation of the herein described kind in the form of atube or sleeve 24 is applied to the rod I6. The parts of the rack abovethe solution level also come into contact with the solution, als the gasarising from the bath as a spray carries with it some of the platingsolution which wets the parts of the racks above the solution-level ofthe bath.

The chromium plating solution is one containing chromic acid, and, toresist the action of the plating solution, I make the insulating blockand tubes 22 and 24 of molded or extruded conjoint polymerization resinhereinbefore described. Blocks, tubes, and also the coatings hereinafterdescribed, of the hereinbefore described conjoint polymerization resinare not attacked by chromium plating solutions containing chromic-acid,such conjoint polymerization resins having the characteristic of notbeing wetted by the platin solution, and hence do not require frequentre-v newals. They are also strong and non-brittle.

In Fig. 2 a xture 3U for re-plating the n'o-gof portion of a go no-gogauge is illustrated. Ther'. go portion of the gauge is stopped" byhaving applied thereto a moulded cap 32 of the hereinbefore describedconjoint polymerization resin which is fitted closely over the goportion of the gauge. A sleeve 34 of the hereinbefore describedpolymerization resin is also preferably applied to the handle part ofthe gauge to stop plating thereon.

In Fig. 3 is illustrated a conventional form of rack 40 for holding aplurality of articles for chromium plating at one time. The rack 40comprises the side-rods (conducting) 42 and 43, to which are connected aseries of cross-rods (conducting) 45, 46, 41, 48, and on thesecross-rods are sets of spring-fingers (conducting) 5U, 5I, which pressand hold the articles (not shown) to be chromium plated. The rack 40 issuspended in the chromium plating solution from a cathode-bus-bar byhooks 55.F vInsulation I0' of the hereinbefore described kind is appliedto the rods 42, 43, 45, 46, 41, 48, to prevent current from passingdirectly from the anodes to the said rods. The insulation I0 is hereshown as a coating 60 resulting from the successive application of filmsor coats of the hereinbefore described conjoint polymerization resin insolution, and drying. In applying the coating 6I) to the metal surface(copper for example) the metal should rst be thoroughly cleaned. Apriming coat should then be applied. The priming coat consists of asolution of the hereinbefore described conjoint polymerization resincontaining a suitable pigment (as d 2,072,170 blue-lead) `forstabilizing the resin during subsequent baking.

i *See page 38, Useful information about lead published by LeadIndustries Association, New York city, 1931.

The priming coat isthen baked on at a suitable Q. temperature.

" hereinbefore described conjoint polymerization `resin are applied byapplying successive coats of iio Thereafter successive coats of the asolution of the aforesaid resin, anddrying.

An example of the method of applying the resin as "a built-up coating,is as followszi 1."A Spray one coat of primer consisting of asolutiorijpf the hereinbeiore described conjoint polymeization resincontaining blueA lead as a stabilizer.

2( Dry 1/2 hour ln air, then bake onehour at 3. Apply one coat bydipping in aclear solution scribed conjoint polymerization resindissolved in a suitable solvent.

4. Dry 1A; hour in air, then force dryone hour in an oven at 150 F. iif.

` 5. 'Apply one coat by dipping in said clear resin solution. 6. Dry 1/2hour in air; then force dry one hour in an oven at 150 F. A

'1. Apply one coat by dipping in said clear resin solution.

` kindiapplied thereto in the form-of a lining or coating T4. Thecoating may be a coating which is built up by spraying or otherwiseapplying coats or lms of the hereinbefore described resin solution, anddrying, as heretofore described, or it may be composed oi. mouldedsheets of the coni joint polymerization resin hereinbefore described.

'The joints 'I6 may be closed in suitable manner,

as by heating the lapped portions of the sheets of the hereinbeforedescribed conjoint polymerization resin to soften them somewhat and thenpressing the lapped portions together; or the i, hereinbefore describedconjoint polymerization i resin in the form of` a powder may be warmedand applied as a putty to the joint; or a thick solution of thehereinbefore described conjoint polymerization resin may be applied tothe joint and subsequently dried. f The tank or tank-lining `foredescribed may also bea `molded monolith of the hereinbeconjointpolymerization resin.

` With atank so constructed straying of current to the sides of the tankwill beavoided and the shading" effect on articles suspended in thesolution, near the si'des for plating, will be avoided.

` .Also there will be no attack on the lining by the i consequently nosludge formation such as results plating solution which contains chromicacid, and

from the attack of chromic acid onthe lead linings of lead-lined tanks.Moreover, with a tank, `such as here provided, there is no metalcontamination of the plating solution, such as results whensolutionsfcontaining chromicacid come into contact with iron, copper,etc. The tanks accordcon'tainlng about 20%.of the hereinbefore de-l ingto this invention are lighter in weight than heretofore, strong, andnon-fragile.

The conjoint polymerization resins as herein described, applied asherein described, will hold their form, and'maintain their resistancetothe action of chromium plating solutions containing chromic acid inthe usual warm baths (temperatures of 35-55 C.) as well as in the coldbaths.

Chromium plating solutions usually contain from about 150 to 500 gramsper liter of chromic acid (CrOa) and catalysts in the form of an acidradical or radicals, such asV sulphate-radical, iiuoride-radlcal(sllico-fiuorides, boro-fluorides), etc. Such solutions may alsosometimes contain other radicals, such as the chloride-radical, etc.Reference is made to Fink Patent #1,581,188 and Fink & McLeese 1 Patents#11,844,751 and #1,928,284, concerning the composition, etc. of chromiumplating baths and methods.

Racks provided with insulation according to this invention havefthefurther advantage that they may be immersed in the usual hot alkalinecleaning solutions frequently employed preliminary to chromium plating,without being destroyed .by such solutions or liquids.

The invention may receive various other embodiments than those hereinspeciiically illus,- trated and described.

What is claimed is:

1. An element or part of a chromium plating `installation which is incontact with a solution containing chromic acid and has insulatingproperties, consistingessentially of a conjoint polymerization resinwhich does not hydrolyze and does not react with such a platingsolution, containing a vinyl compound of the hard resin forming type(consisting of the group vinyl halformingtype, calculated as suchhowever present.

3. A container for a chromium plating solution containing chromic acid,comprising a surface portion in contact with the chromic acid solutionconsisting essentially of a conjointpolymerization resin which does nothydrolyze and does not react with such a plating solution, containing avinyl compound of the hard resin forming type (consisting of the groupvinyl halides, styrene) and a vinyl compound of the soft resin formingtype (consisting of the group of esters of a lower aliphatic acid) therange of the proportions of the two types of compounds in the conjointpolymerization product (calculated as the `monomeric compounds howeverpresent in the resin) being 50 to 95 parts oi vinyl compound or the hardresin forming type to 50 to 5 parts of the vinyl compound of the softresin forming type. i

4. A container for a chromium plating solution containing chromicacid-according to claim 3, in which the range oi the proportions of .theam installation, according to claim 1,'ln which the sal two types ofvinyl compounds is 85 to 8'? parts oi. the vinyl compounds of the hard"resin forminer type and l5 to 13 parts of vinyl compounds of the softresin forming type, calculated as such however present. l

V5. A rack forming an element of a chromium plating installation,comprising insulation on parts thereof in contact with solutionscontaining chrornic acid consisting essentially of a conjointpolymerization resin which does not hydrolyze and does not react withsuch a plating solu tion, containing a vinyl compound of the hard resinforming type (consisting of the group vinyl halide, styrene) and a vinylcompound of the soft resin forming type (consisting of the group ofesters of a lower aliphatic acid) the range of the proportions of thetwo types of compounds in the conjoint polymerization product(calculated as the monomeric compounds however present in the resin)being 50 to 95 parts of vinyl compound of the hard resin forming type to50 to 5 parts of the vinyl compound of the-iso1ft" resin forming type.

6. A rack forming an element of a chromium plating installation,according to claim 5, in which the range of the proportions of the twotypes of vinyl compounds is 85 to 87 parts of the vinyl compounds of thehard resin forming type and 15 to 13 parts of vinyl compounds of thesoit resin forming type, calculated as such however present. l

'7. A rack forming an element of a chromium plating installation,according to claim 5, in v'ihich the insulation consists of built-upfilms or layers of the said resin. i I' GEORGE K. HEazdLGf.v

